The present invention relates to midamble cancellation. More particularly the present invention relates to method and apparatus for performing midamble cancellation utilizing an algorithm enabling parallel cancellation of midamble for both data field 1 and data field 2 of a received TDD burst.
As shown in FIG. 1, a burst is received through a multipath channel having a time-delay spread of (W−1)*Tc, where W represents the number of chips and Tc represents chip duration. The time (delay)—spread channel causes inter-chip interference whereby the convolution tail of each field in the received burst protrudes upon the adjacent field. For example, the midamble inter-chip interference on the first W−1 chips of data field 2 may cause performance degradation of the data estimation procedure of the symbols corresponding to the first W−1 chips, unless a remedy for the interference is considered. This is especially true since the transmit power control (TPC) command (in uplink (UL) only) and transport format combination indicator (TFCI) bits are located immediately after the midamble and they are not protected by any channel coding scheme, it is desirable to eliminate midamble interference by employing a midamble cancellation procedure to improve data estimation for both data parts of the TDD burst and is a stand-alone procedure that can be used to enhance performance of any of the candidate data estimation algorithms.
Midamble cancellation (also referred to hereinafter as MDC) can also be applied to remove midamble interference from the convolution tail of Data field 1 into the first (W−1) chips of the midamble field, also shown in FIG. 1. This tail also results from the delay spread of the multipath channel and its inclusion into the data estimation of Data field 1 results in more observed data and leads to an exact block Toeplitz structure of the AH A matrix in multi-user detection (MUD).